Process of regenerating black liquors



Oct. 28, 1930. v E. G. GooDELL 1,779,537

PROCESS OF' REGENERATING BLACK LIQUORS Filed April l, 1929 DRIED BLACK LIQUOR H NttaSOl FEEDER Edam/1d@ (fooe Patented Oct. 28, 1930 UNITEDv STATES PATENT OFFICE EDWARD G. GOODELL, F STEVENS POINT, WISCONSIN PROCESS OF'REGENERATING BLACK LIQUORS Application led April 1, 1929. Serial No. 351,661.

nace to effect the reduction of the sulphate values to sulphide. I have now found that it is possible to obtain satisfactory reduction eiiiciency by combining my method of spray drying black liquor with the method of spray burning black liquor lsometimes used in sulphate mills.

I-Ieretofore, in spraying a highly concentrated black liquor directly into a smelting furnace for eiecting combustion of the black liquor, it has been found that under the conditions obtainable in the smelting furnace, the eiiiciency of the reduction of the sulphate to sulphide is not entirely satisfactory. This is probably due to the fact that it is diiiicult, if not impossible practically, to maintain the necessary conditions for an eiiicient reduction of the sulphate content to sulphide while at the same time supplying sufficient air for the combustion of the concentrated black liquor.- It will, of course, be understood that while sodium sulphate is added to replace losses in the recovery cycle, its value in this respect is largely dependent upomthe eilicie'ncy of its reduction to the active cooking agent, sodium sulphide.

' fIt-'istherefore an object ofthis invention toupr'ovide an improved process for regeneratm -blackliquors' wherein a portion of the blac `liquor-.to be regenerated is added in the lfjorm' off'a dry product high in or anic contentwhilethe remainder of the lack liquor' is burned Ain a sprayed form.

It isV a', further important object of this invention to provide-.afcombined process of .spray drying'ja'nd,sprayburning black liquor wherein' an.' eilicent'redu'ctionof sulphate to ,sulphide is obtained.

' 1 othemnd jfurthefimpoaant objects' of The general layout of apparatus suited for the carrying out of my process is described in my copending application entitled Meth od of dehydratmg black liquor, Serial No. 351,660, filed April 1, 1929. 'According to my present process, a portion of the black liquor obtained in the manufacture of pulp by the sulphate process is dehydrated in a suitable spray drying chamber or chambers Ito obtain a substantially dry finely divided product high in organic content and heat value. Another portion of the black liquor in a highly concentrated liquid form is introduced directly into a smelting furnace and burned .in spray form under oxidizing conditions. e

Into the same smelting furnace in which the concentrated black liquor is being burned, is introduced a mixture of sodium sulphate and the dried black liquor obtained by my spray drying process. Preferably the sodium sulphate and dried black liquor are in troduced as an intimate admixture into the lower portion of the smelting .furnace below the zone of most active combustion of the sprayed black liquor. Under these conditions, it has been found that a very efficient reduction of the sulphate content, including both the added .sodium sulphate and the metallic sulphate present in the black liquor, is eected.

In the accompanying drawing, which illustrates more or less diagrammatically the means for carrying out my process, the refer.- ence numeral 1 indicates a smelt-in furnace near the bottom of which are positloned one or more tuyeres 2 for. the introduction of'a limited quantity of air to that part of the furnace wherein the*v reduction takes lace. A- highly concentrated solution of blac liquor is sprayed through device 3`to the upper part of smeltingfurnace where additional air 10 to support combustion of said concentrated black liquor is also introduced. Thel gaseous products of combustion escape from passage 4 .to a-fwaste heat boiler 5 fromv l v whichv the hot gases may be led to 'a spray drythis invention will become-apparent from thel following ldescription and v'appende'aill claim..

ingchambeil and auxiliary equipment as de- -the top of the smelting furnace 1 through a vthe sprayed black liquor and consequently mixes with the hot solid particles resulting from such combustion, and the combined solid particles build up upon the floor of the smelting furnace to form a reasonably thick bed of the material, preferably coming up well above the tuyres to give best results. It is in this lower area that the reduction of the vsulphate to sulphide occurs. Under eiiicient operating conditions it has been found possible to produce a smelt containing only 2% unreduced sodium sulphate, whereas 10% of unreduced'slphate is considered good practice when burning black ash according to heretofore used methods, while in the spray burning of black liquor alone the amount of unreduced sulphate 1s generally much higher than in the case of burning black ash.

It appears that the intimate admixture of carbonaceous material present in the dried black liquor with the sodium sulphate serves I to produce the necessary conditions for efficient reduction of the sulphate added in the form of sodium sulphate and present in the black liquor itself. In general, about onethird of the total black liquor is introduced into the smelting furnace in dried form while the remaining two-thirds is introduced by spraying in liquid ferm.

The heat for driving off the Water from the sprayed black liquor to a point at which the black liquor becomes able to support its own combustion is actually furnished by the combustion of the dry, black li uor solids introduced as such into the sme ting furnace. Consequentiy, the sprayed black liquor does not burn entirely or even largely while in suspension but mostly at or slightly above the surface of the bed of molten material that builds up on the fioor of the furnace. In view of this fact and the arrangement whereby the concentrated black liquor is sprayed downwardly upon the bed of molten material, the path of travel of the hot solid particles resulting from the combustion of the sprayed '1 black liquor is comparatively short and consequently losses due to volatilization of the mineral constituents and entrainment of the finely divided solid particles in the stack gases are minimized.

I 'am' aware that' many changes may be made 'and numerous detalls of my process may be varied through a wide range' without dev parting from the principles of this invention,

and I, therefore, do not purpose limiting the patentl granted hereon otherwise than necessitated by the prior art. f

I claim as my invention:

'I he process of regenerating black liquor, which comprises spray burning a portion of black liquor under oxidizing conditions in a zone closely above and near the surface of a bed composed of the solid products of combustion of said black liquorand spray dried black liquor solids introduced as such in admiXture with sodium sulphate, said black liquor solids being at the time of introduction substantially dry and high in organic content, the heat of combustion of said organic content supplying the requisite amount of heat for driving olf the water from said sprayed black liquor to permit combustion .thereof without the use of any foreign fuel and the said organiccontent at the same time serving under the conditions obtaining to effect the reduction of sulphates present in the bed to sulphides.

In testimony whereof I have hereunto subscribed my namevat Stevens Point, Portage County, Wisconsin. l

' EDWARD G. GOODELL. 

